The present invention relates to a shock absorber with leveling function making use of gas pressure used in a four wheel car, a two wheeler and so on, and particularly to a seal construction of a shock absorber with leveling function capable of preventing the gas from leaking out.
As a shock absorber with leveling function, there have been already well known one in which an adjusting nut threadedly inserted into an outer peripheral surface of the body or a cam mechanism is used to support one end of a suspension spring, and the adjusting nut or cam mechanism is operated to adjust the spring force of the suspension spring to high or low, during which leveling is carried out mechanically, or the other in which medium pressure within an outer tube which telescopically receives a shock absorber therein is adjusted to high or low to control the support force exerting on the shock absorber whereby leveling is carried out. Particularly, the former is widely employed actually.
In this case, in the latter, it is difficult to allow a seal member for sealing pressure medium to be sealed into an outer tube to have lubricity, failing to have durability of the seal.
Accordingly, it is an object of the present invention to provide a seal construction of a shock absorber with leveling function capable of improving durability of a seal member for sealing a pressure medium sealed into an outer tube, and capable of preventing the pressure medium from leaking out of a seal present in the shock absorber.
The object of the present invention mentioned above is achieved by a seal construction of a shock absorber with leveling function wherein a seal mechanism is disposed in an outer tube to sidably insert a shock absorber thereinto, a piston rod extending from the shock absorber is connected on the outer tube side, and leveling is carried out while the force of the pressure medium sealed into the outer tube exerting on the shock absorber, the seal construction being constituted that a free piston is interposed opposite to the seal mechanism between the outer tube and the shock absorber, the free piston and the seal mechanism compart and form a lubricating oil chamber therebetween, comprising a bias means for biasing the free piston toward the lubricating oil chamber.
In this case, preferably, a seal element in sliding contact with the outer circumference of the shock absorber is provided on the end on the lubricating oil chamber side of the free piston.
Likewise, preferably, the bias means for urging the free piston comprises a differential pressure spring.
Likewise, preferably, a seal case is connected to an upper end of the outer tube, a seal mechanism comprising a bearing member provided with a seal element in sliding contact with an outer circumference of the shock absorber is provided in an inner circumference at the upper end of the seal case, likewise, a free piston provided with a seal element inwardly of the bearing member is provided internally of the seal case, a differential pressure spring for biasing the free piston upward is provided between a lower part of the seal case and the free piston, and a lubricating oil chamber is comparted between the bearing member and the free piston.
Being constituted as described above, lubricating oil can be supplied to the seal mechanism, and durability of seal is improved. In addition, even if lubricating oil is leaked out, lubricating oil is supplied to the seal mechanism without fail since the free piston is biased.
Further, pressure of lubricating oil sealed into the lubricating oil chamber is always maintained high by a portion of the force by which the free piston presses lubricating oil within the lubricating oil chamber by the biasing force of the bias means, as compared with pressure of the pressure medium within the outer tube comparted with the free piston interposed between the outer tube and the shock absorber.
In this manner, it is possible to positively prevent the pressure medium from leaking out through the lubricating oil chamber located outwardly thereof by always maintaining oil pressure of the lubricating oil chamber high by a portion of predetermined pressure to thereby prevent the pressure medium from being gasified and leaking out from a clearance present in the shock absorber.